In one particularly harrowing incident, a terrorist encounters a group of people huddled together in fear in a narrow corridor. After calmly approaching them he hurls a grenade and runs - with his terrified victims scattering in panic or falling dead or injured amid the resultant explosion.

Al-Qaeda has stepped up its attacks against Yemeni security forces in recent years - though these attacks have been mainly in the lawless southern and eastern provinces where extremist groups are active - taking advantage of the weakening of the central government in Sana’a since a popular uprising that toppled president Ali Abdullah Saleh in 2011.